The present invention relates to the diagnostic imaging arts. It finds particular application in conjunction with SPECT nuclear imaging systems and will be described with particular reference thereto. It will be appreciated, however, that the present invention is useful in conjunction with other systems that utilize collimated detectors to detect penetrating radiation, and is not limited to the aforementioned application.
In nuclear imaging, a source of radioactivity is used to provide non-invasive diagnostic images. The source is typically injected into a patient, although external sources are also utilized. Radiation from the source traverses at least a portion of the patient and is detected by radiation detectors.
Typically, a nuclear camera has one, two, or three detector heads. In rotating laminar emission cameras (ROLEC), a one-dimensional detector array or line of detectors is rotated in each head. Collimator vanes which are mounted between the detectors of the array rotate with the detector array. In rotating laminar emission cameras, the one-dimensional collimation results in a plane integral reconstruction as opposed to a line integral reconstruction, as is typical in most Anger camera systems. This distinction illustrates a particular difference between one-dimensional and two-dimensional collimation. In a system collimated in one dimension, the detector xe2x80x9cseesxe2x80x9d that is, receives radiation from, a plane. In a typical Anger camera with two dimensional collimation, each collimated element of the detector sees a line of the imaging volume. Moreover, described more accurately, the typical ROLEC produces only an approximation of a planar integral.
In actuality, the plane integral should have a weighting factor included therein in order to compensate for a 1/r dependence to an object being imaged, where r represents the distance of a detectable radiation event to the detector. All other things being equal, the detector is more sensitive to relatively close objects, and is less sensitive to relatively distant objects. Typically, previously developed ROLECs ignore the 1/r weighting, accepting that the detected information is an approximation. Ultimately, failure to model the dependence, or improper modeling of the dependence reduces resultant image quality.
The applicants earlier copending application Ser. No. 09/708,960 discloses a reconstruction system which corrects for the 1/r dependence. The parallel collimator vanes are skewed a few degrees from perpendicular. When the detector array is rotated to 180xc2x0 opposite orientations, a pair of corresponding data sets are generated whose planes are offset by a very small but known angle. As explained in detail in the aforesaid copending application, this relationship enables the 1/r dependency to be reduced to a trigonometric function of the angle, which is a constant.
Unfortunately, these relationships were limited to substantially parallel collimator geometries. Like earlier ROLEC reconstructions, data from magnifying (converging) collimators and minifying (diverging) collimators could not be reconstructed accurately.
The present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others.
In accordance with one aspect of the present invention, a method of diagnostic imaging is provided. A radioactive isotope is introduced into a subject in an imaging region. The radiation is detected by a rotating solid state detector array generating a plurality of planar images. The detector array is moved about a longitudinal axis of the subject. The detector array is collimated by a non-parallel slat collimator in either a convergent or divergent formation. The detected photon emissions are reconstructed into an image representations of the subject.
In accordance with another aspect of the present invention, a diagnostic imaging apparatus is given. A means for detecting detects radiation that is transmitted through at least a portion of a subject in an imaging region. A collimating means collimates the radiation. A first rotating means rotates the detecting means about an axis perpendicular to a main longitudinal axis of the subject. A second rotating means rotates the detecting means about the longitudinal axis. A means for reconstructing reconstructs the detected radiation into an image representation.
In accordance with another aspect of the present invention, a SPECT camera is provided. A detector head that includes a linear array of detector elements and a magnifying collimator is mounted for movement about an axis of a subject. A motor rotates the array around a detector axis of rotation. A reconstruction processor reconstructs signals from the detector into an image representation.
In accordance with another aspect of the present invention, a method of nuclear imaging is provided. A linear detector array and a convergent collimator are rotated about a detector axis of rotation and around a subject axis of rotation. Radiation from the subject is converted into electrical signals which are reconstructed to form a magnified image representation.
One advantage of the present invention resides in a magnifying detector assembly.
Another advantage resides in sub-millimeter resolution.
Another advantage of the present invention is that it presents a small, relatively light nuclear detector array.
Yet another advantage is that it presents a solid state nuclear detector array.
A further advantage resides in minifying collimation with accurate reconstruction.
Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.